TL;DR
Special days can add a label, alter the cycle or select a different bell schedule. A reusable definition may affect several dates.
Steps
In Calendar, review the bell schedules assigned to weekdays and the available special days.
Create or edit the bell schedule needed for the event, checking times and schedule tags.
Create a special-day definition and choose its calendar and bell-schedule effects.
Apply it to the intended dates, inspect the resulting periods, then save.
Before editing an existing definition, check every date using it. Create a separate definition for a one-off exception. Matching schedule tags connect bell times to section schedules; a missing match can make periods disappear.
Related help
Configure section schedules and resolve conflicts · Handle closures and cycle changes · Display exam schedules
